Natural silk insulated electric conductor



June 3o, 1953 w. TRAVIS n 2,644,029

NATURAL SILK INSULATED ELCTRIC `CQNDUCTQR Filed J\l1ly 27, 1949 Attorneys Patented June 30, 1953 NATURAL SILK INSULATED- ELECTRIC CONDUCTOR William Travis, Southport, England, assigner to Cennollys (Blackley) Limited, Manchester,

England, a British company Application July Z7, 1949, Serial No.' 107,115 In Great Britain August `16, 1948 (Cl. 17e-124.)

S Claims. l

This invention relates to insulated electric conductors in which the insulatingv ycovering comprises one or more layers of natural silk.

Raw silk contains approximately of the natural gum sericin. Natural silk normally used for insulating electric conductors is raw silk which has been treated by a process known as degumming or boiling oli by which substantially all of the sericin is removed. This process the associated operations of rewinoling and throwing the rtreated silk increase its cost conn siderably.

The object of the present invention is to provide an improved. silk covered wire which is economically and simply manufactured.

In accordance with the invention the coven ing comprises one or more layers of natural silk in which the major proportion of the naturally occurring sericin gum is retained. Sericin ring is an insulant, is chemically neutral and is not readily soluble, almost the only effective solvents being hot water and hotaqueous solutions. The silk is applied by lapping directly onto the conductor or over a layer of another insulating inaterial e. g. enamel. Further layers of insulation may be applied over the silk layer or layers. The term conductor as used herein includes single conductors such as a wire or strip and multiple conductors made up from a number of wires stranded or hunched together.

`Before application to theconductor the'sericin gum in the silk is softened by a process which includes immersion in hot water. To maintain this soft condition until and during the lapping operation, the silk iskept wet. Since sericin gum is soluble in hot water a small vproportion. of .the naturally occurring gum may be removed during the softening process but infall cases the major proportion Aof the gum is retained.

The natural lsilk containingr the gum is obtained in the form of hanks or skeins; it is pre ferred to wind the sil-k thread from the hanks or skeins in the form of cheeses or onto spools before softening the gum .by treating the cheeses or spools with water. While the .silk is wet and the sericin soit the filaments or" silk spread evenly on to the conductor to which they are applied.

The thorough softening of the gum by imn mersion of the silk in hot water is facilitates by a preliminary impregnation with water. A quantity of the silk wound on a suitable sup port, for example in the form of a cheese or on a spool, is enclosed in an evacuated chamber so as to remove as far as possible the air entrapped in its interstices. Suiiicient water is then alf from the spoolonto the wire.

lowedto enter' the chamber to immerse thesilk This preliminary treatment ensures that water reaches al1 the libres of the silk throughout the whole of the cheeseor spool. Altogether in this impregnation process and the subsequent hot water treatment the silk absorbs at least 1.09% by weight of water.

The preferred process of preparing the silk and applying it to a wire is hereinafter described asfan example, with reference to the accompany ing drawings in which Figure l is an elevation of agshort length of the insulated conductor and Figure 2 is an elevation, partly in cross-section of a lapping head. The natural silk, obtained in the form of hanks or skeins, is wound onto cheeses or spools, appropriate precautions being taken to allow' for the expansion of the silk during the softening process. If the silk is wound in the form of a cheese, that is on a plain tube, no special precautions are necessary but if ordinary spools are used it is necessary to wind the silk with sufiicient interstices to accommodate the absorbed water. Alternatively, it is 'possible to use spools having flanges which are movable axially to allow for-expansion of the silk.

The cheeses or spools. are enclosedin a chainu ber which is iirst evacuated. and then filled with suicient water to immerse them. From this chamber they are transferred while still wet to a vessel containing water at a temperature of -l00 C. in which they remain until the gum is thoroughly softened. The softening normally takes about. two hours but if lower temperatures are used, say 70 C., although satisfactory softn ening is possible, the time taken is considerably increased. This completes the'softening process in which the silk absorbs at least of weight'of water. Until required the silk is ke under cold water to keep the gum soft. lt is found that the gum will remain soft vfor long periods without deterioration.

The silk is lappedonto the wire in a machine of the kind .in which the wire passes axially through the cheese or spool. and the cheese or spool is positively rrotated about the wire, silk being unwound by a flier which is free to rotate about the axis of the wire, subject to the exerH .tion of a small frictional force between the flier and the spool, or a support for the spool. The dier extends across one end of the spool and projects radially outwards beyond the edge ci the spool, carrying on its outer end an eye or guide through which the silk passes in its passage The pull exerted by thesilk on the ilier'as it is Wound on the wire accenno 3 causes the flier to rotate relative to the spool and unwrap the silk from the spool. The rate of relative movement is .small compared with the rate of rotation of the head.

It will be seen that the tension to bc by the silk is comparatively srnall. lt depends on friction, windage and inertia of the flier. inay be controlled by the design and selection oil the materials so that the tension becomes of very small value. It is preferable to in o the unavoidable forces and to apply extra and adjustable tension by increasing the force of friction between the iiier and the spool. This additional force may be applied by a spring arm pressing axially on the hier but not rotating with it and having its spring force adjustable.

The flier may be attached to and rotate with a device for guiding the silk onto the conductor. This may include a die and a spreader i. e. a riot bar with a narrow edge over which the silk is spread in the forni of a ribbon. The lapping head is mounted in an enclosure and during the lao1 ping operation the silk is kept wet by an atom-.iced water spray arranged inside the enclosure. Ey means of this spray the humidity inside the closure is maintained at 100%.

Referring to liigure l of the ldrawings which shows the lapping head of a machine of the kind preferred, the wire l passes from a supply spool vertically upwards through a hollow spindle 2 rotated in known manner by a pulley 3 and carr rying on its upper end a plate @n the plate l is hired a support 5 for the silk cop l. The support 5 is formed with a cylindrical recess l in which lits a downward extension t of a hub il which carries a flier lil. A die il and bar l2 are also carried on the hub sill-z thread El passes from the cop d, through an eye i3 on the end of the flier lil, over the spreader bar lll is guided. onto the wire l by the die The covered wire passes upwards through a drying oven lil onto a take-up spool of normal construction. The head surrounded by a fixed enclosure l5 water supply pipe le from which an atoinised spray ci water is directed onto the cop o.

Figure 2 shows a length of the covered con ductor consisting of a copper wire i covered with a single lapping of silk 2 from which the naturally L occurring sericin gum has not been removed.

.Although it has been found that this form of lapping machine is particularly suitable for use in. the process of the present invention, especially when lapping very ne silk thread onto conductors, it is also possible to use the standard form oi machine normally used for lapping silk onto conductors. In the standard rnachine the cop or spool is mounted on a rotating head which also carries the die and guides for directing the silk thread onto the conductor. The cop or spool is caused to rotate relatively to the head to un wind the silk by the tension of the silk. This tension may be comparatively large.

After the wet silk has been lapped onto the conductor it is thoroughly dried before use. The silk-covered conductor may be passed through. a hot Zone before being wound onto the take--up spool or hot air may be blown onto it as it is wound on the take-up spool. Alternatively, the spool can be removed from the machine when full and vacuum dried. v

The insulated conductors of the present invention have the advantages that they are cheaper than known forms of silk insulated conductors in through one wall of which passes a view of the use of less expensive silk and can be manufactured at higher speed. rlhis latter advantage is obtained because the silk containing sericin can be lapped on with a longer lay than is usual with degurnrned silk. The degummed silk must be applied to the wire with a lay that the silk does not readily unwind itself from the conductor or run back when the conductor is cut. However long the lay of the silk containing gurn this will not occur since there is a slight adherence between the silk and the conductor, which is sufficient to prevent the sill: running back when the conductor is cut.

What I claim as my invention is:

l. The method of manufacture of an insulated electric conductor which comprises inersing a quantity of silk, in which at least the major proportion of the naturally occurring sericin gum is retained, in hot water, thereby softening the gum, and lapping said silk, while still wet, helically round a conductor.

2l. The method of manufacture or an insulated electric conductor which comprises iininersing a quantity of silk, in which at least the major proportion of 'the naturally occurring sericin gum is retained, in hot water, thereby softening the gum, le L ing said r helio-ally roiilnd a ce doctor, while acted upon by an atornised water spray.

3. The method of manufacture of an insulated conductor which comprises enclosing a quantity of natural silk, in which the major proportion of the sericin gum is retained, in a chamber, evacuating said charnoer, covering said silk with water, treating said silk with hot water whereby i l gum is softened and lapping said silk while 'l wet helically round a conductor.

An electric conductor provided directly on the surface thereof with an insulating covering consisting of a helically lapped layer of natural silk threads in which the major proportion of the naturally occurring sericin gum is retained, said sericin gum bonding said threads together.

5. An electric conductor provided with at least one layer of a solid insulating material and, di'- rectly on the surface of the outermost of said layers, a further insulating covering consisting of a helically lapped layer of natural silk threads in which the major proportion of the naturally occurring sericin gurn is retained, said sericin gum bonding said threads together.

6. An insulated electric conductor consisting of a single wire provided directly on the surface thereof with at least one helically lapped layer of natural silk threads in which the major pro portion of the naturally occurring sericin gum is retained, said sericin gum bonding said threads together.

7. An insulated conductor consisting of an enamelled wire and, directly on the surface of the enamel, at least one helically lapped layer of natural silk threads in which the major proportion of the naturally occurring sericin gum is retained, said sericin gum bonding said threads together.

8. The method of manufacture of insulated electric conductor which comprises softening the sericin gum in raw silk threads in which the major proportion of the naturally occurring sericin gum is retained and lapping said threads in a wet state helically round a conductor.

WILLIAM TRAVIS.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Splitdorf Dec. 14, 1875 5 Rueter Apr. 26, 1892 Lenher Aug. 27, 1935 Dreyfus Feb. 16, 1937 Goodings Feb. 22, 1938 Cork Feb. 24, 1948 10 OTHER REFERENCES Bleaching, Dyeing and Chemical Technoogy of Textlle Fibres, 2d edition, 1946, by S. R. Trotman. Page 146, lines 3 and f1.A 

4. AN ELECTRIC CONDUCTOR PROVIDED DIRECTLY ON THE SURFACE THEREOF WITH AN INSULATING COVERING CONSISTING OF A HELICALLY LAPPED LAYER OF NATURAL SILK THREADS IN WHICH THE MAJOR PROPORTION OF THE NATURALLY OCCURRING SERICIN GUM IS RETAINED. SAID SERICIN GUM BONDING SAID THREADS TOGETHER. 